1. Field of the Invention
The subject matter of the present disclosure relates to the field of continuously variable transmissions (CVT), generally. More specifically, this invention relates to torque-responsive driven elements of belt-type continuously variable transmissions. Most specifically, the invention is a variable pitch driven sheave for operative interconnection by a V-belt with a speed responsive drive sheave to form a variable ratio rotary power transmission system.
The drive (or secondary) sheave element described here may be incorporated into a belt-type continuously variable transmission (CVT) comprising a speed-responsive drive (or primary) sheave, a V-belt, and a torque-responsive driven sheave. An embodiment of the continuously variable transmission driven element of the present disclosure ("driven sheave") is an improved, torque-responsive, CVT secondary sheave that is suited for use in snowmobiles, all-terrain vehicles (ATV's), and in other vehicular and stationary applications.
2. Description of the Prior Art
U.S. Pat. No. 5,720,681 issued Feb. 24, 1998, to Benson for a Torque Responsive Actuation Device. Benson discloses a three-surfaces cam similar to the disclosure of Laughlin, Deschene, and Butterfield et al (U.S. Pat. Nos. 3,605,510, 3,605,511 and 4,216,678, respectively). Benson applies crowned, or laterally radiused, rollers similar to those shown by Steuer (U.S. Pat. No. 3,722,308) to improve driven sheave performance. Sheave faces are biased toward the initial, or minimum separation position by a torsion spring.
U.S. Pat. No. 4,969,856 issued Nov. 13, 1990, to Miyata et al for a Pulley-Type Speed-Shifting Device. Miyata et al discloses a pulley-type transmission that can be manually set at any desired ratio. The structure of the cam follows is similar to that of the disclosed driven sheave cam follower in that a spider with two rollers is used to set the separation of the sheave halves. Engine braking is provided with this transmission system by a tensioner that prevents belt disengagement during operation.
U.S. Pat. No. 4,523,917 issued Jun. 18, 1985, to Schildt for a Variable Pitch Diameter Torque Sensing Pulley Assembly. Schildt discloses a cam-actuated torque-responsive pulley that has two steps in the cam angles. When the sheave faces are between their greatest separation and mid-range (i.e., the effective diameter is small), a low cam angle (e.g., 30.degree.) causes a high axial force to be applied to the belt. When the sheave faces are between mid-range and their closest, the axial force applied against the belt is lower because the cam angle is steeper (e.g. 45.degree.). The cams and cam followers are symmetrical making the pulley bi-directional. An example of the use of the pulley as a drive pulley is given in which the driven pulley is fixed-pitch. The ratio of that system is varied by changing the distance between the driving and the driven shafts.
U.S. Pat. No. 4,378,221 issued Mar. 29, 1983 to Huff et al for a Torque Cam Assembly for Variable Speed Drive and Follower Element therefor. Huff et al disclose a driven sheave that can operate rotating in either direction. Also described is a cam surface-contacting plastic wear button that has a quicker break-in time than some earlier buttons.
U.S. Pat. No. 3,722,308 issued Mar. 27, 1973 to Steuer et al for a Bearing of the Conical Discs of an Infinitely Variable Cone Pulley Transmission. Steuer discloses an improved shape for the rollers that transmit power from the moveable sheave element to the driven shaft. The attempt is to overcome wear of the rollers and inclined ramps on which the sheave spacing adjustment rollers operate. It may be that the design of the disclosed driven sheave element reduces the need for the remedy disclosed by Steuer.
U.S. Pat. No. 3,605,511 issued Sep. 20, 1971 to Deschene for a Self-Cleaning Centrifugal Clutch. Deschene discloses a radially grooved shaft between the two faces of the CVT drive split sheave disclosed by Laughlin. The grooves are said to reduce belt wear when the engine is idling and the vehicle is stopped. In addition, any build-up on the shaft is cleared by operation of the drive sheave.
U.S. Pat. No. 3,365,967 issued Jan. 30, 1968 to Moogk for a Stepless Variable V-Belt Driving Gear With Asymmetric V-Belt. Moogk discloses a pair of rollers that contact cams to maintain constant speed in response to varying torque. A compression spring provides a biasing force against which the rollers and cams act.
U.S. Pat. No. 2,900,834 issued Aug. 25, 1959, to Bessette for an Automatic Variable Speed Pulley. Bessette discloses a V-belt pulley that automatically adjusts the effective diameter of the pulley in accordance with the load applied to it. A moveable split sheave face is moved toward a fixed sheave face by cams acting against radially extending pins. A torsion spring biases the sheave faces toward the initial or starting condition. Rollers in complementary inclined tracks or grooves can be used in place of the pins and cams.
U.S. Pat. No. 2,623,400 issued Dec. 30, 1952, to Davis for a Power Transmission and Centrifugal Clutch. Davis discloses a centrifugal clutch that moves split drive sheave faces toward each other to engage a V-belt. A spring-loaded driven split sheave serves as a belt-tightener.
U.S. Pat. No. 2,276,186 issued Mar. 10, 1942, to Getchell for a Pulley Construction. Getchell discloses a split-sheaved pulley that is much more complex than the design disclosed herein. Both halves of the sheave are moveable on the shaft and all power is transmissed through a spider keyed to the end of a shaft.